History is often divided into "ages" (aeons), which are time periods each with certain commonalities. One age comes to an end and a new age or world to come, where different realities are present, begins. When such transitions from one age to another are the subject of eschatological discussion, the phrase, "end of the world", is replaced by "end of the age", "end of an era", or "end of life as we know it". Much apocalyptic fiction does not deal with the "end of time" but rather with the end of a certain period of time, the end of life as it is now, and the beginning of a new period of time. It is usually a crisis that brings an end to current reality and ushers in a new way of living, thinking, or being. This crisis may take the form of the intervention of a deity in history, a war, a change in the environment, or the reaching of a new level of consciousness.

Most modern eschatology and apocalypticism, both religious and secular, involve the violent disruption or destruction of the world; whereas Christian and Jewish eschatologies view the end times as the consummation or perfection of God's creation of the world. For example, according to ancient Hebrew belief, life takes a linear (and not cyclical) path; the world began with God and is constantly headed toward God’s final goal for creation, which is the world to come.

Eschatologies vary as to their degree of optimism or pessimism about the future. In some eschatologies, conditions are better for some and worse for others, e.g. "heaven and hell".

In Bahá'í belief, creation has neither a beginning nor an end.[3] Instead, the eschatology of other religions is viewed as symbolic. In Bahá'í belief, human time is marked by a series of progressive revelations in which successive messengers or prophets come from God.[4] The coming of each of these messengers is seen as the day of judgment to the adherents of the previous religion, who may choose to accept the new messenger and enter the "heaven" of belief, or denounce the new messenger and enter the "hell" of denial. In this view, the terms "heaven" and "hell" are seen as symbolic terms for the person's spiritual progress and their nearness to or distance from God.[4] In Bahá'í belief, the coming of Bahá'u'lláh, the founder of the Bahá'í Faith, signals the fulfilment of previous eschatological expectations of Islam, Christianity and other major religions.[5]

Some forms of Buddhism hold a belief in cycles in which the life span of human beings changes according to human nature. In the Cakkavati sutta, the Buddha explained the relationship between life span of human beings and their behaviour. According to this sutta, unwise behavior was unknown among the human race in the past. As a result, people lived for an immensely long time — 80,000 years — endowed with great beauty, wealth, pleasure, and strength. Over the course of time, though, they began behaving in various unwise ways. This caused the human life span gradually to shorten, to the point where it now stands at 100 years, with human beauty, wealth, pleasure, and strength decreasing proportionately.[citation needed]

Ultimately, conditions will deteriorate to the point of a "sword-interval," in which swords appear in the hands of all human beings, and they hunt one another like game. A few people, however, will take shelter in the wilderness to escape the carnage, and when the slaughter is over, they will come out of hiding and resolve to take up a life of wise and virtuous action again. With the recovery of virtue, the human life span will gradually increase again until it reaches 80,000 years, with people attaining sexual maturity at 500.[citation needed]

According to Tibetan Buddhist literature, the age of the first Buddha was 1,000,000 years and his height was 100 cubits while the 28th Buddha, Siddhartha Gautama (563BC–483BC) lived 80 years, and his height was 20 cubits.[citation needed]

In other traditions, such as Zen, a somewhat utilitarian view is taken. The notion often exists that within each moment in time, both birth and death are manifest. As the individual "dies" from moment to moment, they are equally "reborn" in each successive moment, in what one perceives as an ongoing cycle. Thus, the practitioner's focus is shifted from considerations regarding an imagined future endpoint, to mindfulness in the present moment. In this case, the worldview is taken as a functional tool for awakening the practitioner to reality as it exists, right now.[citation needed]

The Second Coming of Christ is the central event in Christian eschatology. Most Christians believe that death and suffering will continue to exist until Christ's return. There are, however, various views concerning the order and significance of other eschatological events.

The book of Revelation is at the core of Christian eschatology. The study of Revelation is usually divided into four approaches. In the Futurist approach, Revelation is chiefly seen as referring to events which as yet have not come to pass, but which will come to pass at the end of the age, and the end of the world. This is the approach which most applies to eschatological studies. In the Preterist approach, Revelation chiefly refers to the events of the first century, such as the struggle of Christianity to survive the persecutions of the Roman Empire, the fall of Jerusalem in 70 AD, and the desecration of the temple in the same year. In the Historicist approach, Revelation provides a broad view of history, and passages in Revelation are identified with major historical people and events. In the Idealist (or Spiritualist or Symbolic) approach, the events of Revelation are neither past nor future, but are purely symbolic, dealing with the ongoing struggle and ultimate triumph of good over evil.

Contemporary Hindu eschatology is linked in the Vaishnavite tradition to the figure of Kalki, the tenth and last avatar of Vishnu before the age draws to a close who will reincarnate as Shiva simultaneously dissolves and regenerates the universe.

Most Hindus believe that the current period is the Kali Yuga, the last of four Yuga that make up the current age. Each period has seen successive degeneration in the moral order, to the point that in the Kali Yuga quarrel and hypocrisy are the norm. In Hinduism, time is cyclic, consisting of cycles or "kalpas". Each kalpa lasts 4.1 - 8.2 billion years, which is a period of one full day and night for Brahma, who in turn will live for 311 trillion, 40 billion years. The cycle of birth, growth, decay, and renewal at the individual level finds its echo in the cosmic order, yet is affected by vagaries of divine intervention in Vaishnavite belief. Some Shaivites hold the view that Shiva is incessantly destroying and creating the world.

After this larger cycle, all of creation will contract to a singularity and then again will expand from that single point, as the ages continue in a religious fractal pattern.[6]

Islamic eschatology is documented in the sayings of the ProphetMuhammad, regarding the Signs of the Day of Judgment. The Prophet's sayings on the subject have been traditionally divided into Major and Minor Signs. He spoke about several Minor Signs of the approach of the Day of Judgment, including:

Abu Hurairah reported that Muhammad said: "If you survive for a time you would certainly see people who would have whips in their hands like the tail of an ox. They would get up in the morning under the wrath of God and they would go into the evening with the anger of God."[7][8]

Abu Hurairah narrated that Muhammad said, "When honesty is lost, then wait for the Day of Judgment." It was asked, "How will honesty be lost, O Messenger of God?" He said, "When authority is given to those who do not deserve it, then wait for the Day of Judgment."[9]

'Umar ibn al-Khattāb, in a long narration, relating to the questions of the angel Gabriel, reported: "Inform me when the Day of Judgment will be." He [the Prophet Muhammad] remarked: "The one who is being asked knows no more than the inquirer." He [the inquirer] said: "Tell me about its indications." He [the Prophet Muhammad] said: "That the slave-girl gives birth to her mistress and master, and that you would find barefooted, destitute shepherds of goats vying with one another in the construction of magnificent buildings."[7][9]

"Before the Day of Judgment there will be great liars, so beware of them."[9]

"When the most wicked member of a tribe becomes its ruler, and the most worthless member of a community becomes its leader, and a man is respected through fear of the evil he may do, and leadership is given to people who are unworthy of it, expect the Day of Judgment."[9]

Regarding the Major Signs, a Companion of the Prophet narrated: "Once we were sitting together and talking amongst ourselves when the Prophet appeared. He asked us what it was we were discussing. We said it was the Day of Judgment. He said: 'It will not be called until ten signs have appeared: Smoke, Dajjal (the Antichrist), the creature (that will wound the people), the rising of the sun in the West, the Second Coming of Jesus, the emergence of Gog and Magog, and three sinkings (or cavings in of the earth): one in the East, another in the West and a third in the Arabian Peninsula.'" (note: the previous events were not listed in the chronological order of appearance)

The Sun will turn into a red giant in approximately 5 billion years. This red giant Sun will have a maximum radius beyond the Earth's current orbit. The Sun's expansion will not lead to the end of the Universe; its effects will be limited to the Solar System. Life on Earth will become impossible due to a rise in temperature long before the planet is actually swallowed up by the Sun.[14]